W bosonA subatomic particle with positive electric charge that mediates the weak nuclear force. The W boson has a mass 160,000 times that of the electron. Unlike the other weak force mediator (the Z boson), the W boson changes particles it interacts with into other kinds of particles; for example, in beta-plus decay(a kind of beta decay), an up quark in a proton decays into a down quark by emitting a W boson, changing the proton into a neutron. The W boson itself decays into a positron and an electron neutrino. See Table at subatomic particle.